The present invention relates to a cooling device for dissipating the heat generated by semiconductor elements or integrated circuit chips.
In a large-sized electronic computer system, it is demanded that the processing operation is performed at high speed. To this end, a circuit chip on which a large number of semiconductor elements are integrated has been developed in recent years. Further, in order to make short the electric wiring for interconnecting such integrated circuit chips, a method of mounting a large number of such integrated circuit chips in a micropackage is developed.
A cooling device which is disclosed in U.S. Pat. No. 3,993,123 has hitherto been proposed with regard, in particular, to a cooling device for use in the large-sized electronic computer system. In this cooling device, the heat generated by LSI chip is transferred into a piston via the helium-gas layer which exists around a portion of contact between a spherical tip end of the piston and a back planar surface of the LSI chip. The heat is then transferred from the piston into the helium-gas layer which exists in the clearance between this piston and a cylinder, thus transferred into a housing of a micro package. The heat is thus finally introduced, for dissipating, into a cooler which is provided on the housing and in which cooling water or cooling air is circulated.
The above-mentioned prior art cooling device, however, involves the following problems.
Thermal conductivity of helium-gas is relatively high as compared with other gases, but its thermal conductivity is very low as compared with that of a metallic body such as, for example, the piston, cylinder or the like. Accordingly, in order to make the thermal resistance of the layer of helium gas small, it is necessary to make the clearance between the piston and cylinder small. For this reason, the piston or cylinder is demanded to be fabricated with high precision. If it is fabricated with low precision, then, for example, the piston fails to be moved with smoothness, or the temperature of each LSI chip is likely to vary widely.
A cooling structure such as that disclosed in U.S. Pat. No. 4,263,965 has been proposed in order to solve the above-mentioned problems. In this structure, a number of parallel grooves are formed in a housing opposed to the LSI chips, and, in each groove, a thin rectangularly shaped thermal conductive plate and a leaf spring for applying a pressing force onto this thermal conductive plate are inserted. This structure is improved in that the surface area for effecting a heat exchange between the thermal conductive plate and the side walls of the parallel grooves is large and besides the thin planar surface of each thermal conductive plate is kept in plane contact with the planar surface of LSI chip at its one end surface.
The above-mentioned structure, however, involves the following problems. Since each thermal conductive plate is independently separated and inserted into its corresponding parallel groove, the heat exchange between adjacent thermal conductive plates is little effected. Since the integrated circuits on the LSI chip are composed of a number of electric circuits, it is, generally, very rare that such LSI chip generates heat uniformly. The distribution of heat generation in the LSI chip varies from place to place, as well as with the lapse of time. Accordingly, only the thermal conductive plate located near such peripheral portion serves to a portion of heat generation on the LSI chip dissipate the heat generated therefrom. In other words, the other thermal conductive plates which are located away from such portion of heat generation can serve to dissipate only the heat which has come via the LSI chip having a very small thickness. Namely, even if a number of thermal conductive plates are placed on the LSI chip, their efficiency of heat dissipation is decreased because the good heat transfer connection between these thermal conductive plates is little effected.
Further, since the maximum size where the thermal conductive plates can be mounted is limited by a width of the LSI chip, limitation is imposed upon increasing the cooling performance.
Further, a cooling device which uses a thermal conductive metallic plate bundle composed of laminated leaf springs is disclosed in Japanese Patent Laid-Open No. 23463/83. This cooling device has a drawback in that the thermal contact resistance between the leaf springs is high.